The invention relates to radiotherapy, and more particularly relates to image-guided radiotherapy (“IGRT”). In its most immediate sense, the invention relates to a quality-control jig for use with IGRT apparatus.
In IGRT apparatus, two instruments are mounted upon a rotatable gantry. One of these is a linear accelerator (a “linac”). The linac produces a beam of high-energy radiation (the “treatment beam”) used to destroy tumor tissue inside the patient's body. The other is an imager (which is usually but not necessarily a cone-beam computed-tomography imager). This produces a lower-energy beam of radiation (the “imaging beam”) used to create a three-dimensional image of the patient's body region in which the patient's tumor is located. The linac's treatment beam and the imager's imaging beam are at right angles to each other.
Before a patient is imaged and subjected to radiation therapy, it is necessary to make sure that the IGRT apparatus is properly calibrated. This is because IGRT apparatus operates neither with theoretical perfection nor with absolute repeatability.
For these reasons, radiation technicians routinely carry out quality-control procedures on IGRT apparatus before patients are imaged and subjected to radiation therapy. This enables the technicians to monitor the actual performance of the IGRT apparatus and to make sure that the apparatus is properly calibrated. However, such procedures are time-consuming and complicated.
It would be advantageous to provide a jig that would make it easier to carry out quality-control procedures on IGRT apparatus, and to make it possible to carry out those procedures more quickly.
Objects of the present invention are to provide a jig that facilitates and speeds the performance of quality-control procedures on IGRT apparatus.
The invention proceeds from the realization that a ball bearing that is used to carry out a common quality-control procedure can be incorporated as a detachable part of a jig that can be used to check other apparatus parameters by shining light on the jig.
In accordance with the invention, a jig has an elongated stylus with a proximal end and a distal end. The proximal end of the stylus is secured to a three-axis positioner.
A ball bearing is provided, as is a ball bearing cap that is secured to the ball bearing and adapted to fit over the distal end of the stylus to detachably mount the ball bearing thereto. A pointer having a distal tip is provided, as is a pointer cap that is secured to the pointer and adapted to fit over the distal end of the stylus to detachably mount the pointer thereto. The ball bearing, the ball bearing cap, the pointer, and the pointer cap are all dimensioned such when the pointer cap is mounted to the distal end of the stylus, the distal tip of the pointer has the same location as does the center of the ball bearing when the ball bearing cap is mounted to the distal end of the stylus.
A flat plate is provided, as are means for fixing the plate to the stylus in such a manner that the pointer will cast a shadow on the plate when a light is directed onto the pointer from a direction normal to the plate.
This jig makes it easy to carry out many commonly-performed quality-control quickly and efficiently. Once the positioner has been used to place the ball bearing at the calculated radiation isocenter of the IGRT apparatus, measurements of other apparatus parameters can be carried out relative to the known position of the radiation isocenter by directing light onto the jig.
Advantageously, the fixing means is adapted to fix the plate to the stylus at a 0° orientation, a 90° orientation, a 180° orientation, and a 270° orientation. This allows the jig to be conveniently reconfigured for use at four gantry positions. Likewise advantageously, an axially-elongated hollow phantom is provided. The phantom is detachably securable to the positioner in a manner that the stylus extends along the axis of the phantom and has surface markings indicating locations that are axially aligned with the center of the ball bearing and that are also rotationally aligned with gantry orientations of 0°, 90°, and 270°. This makes it possible to align the lasers used to position the patient. Additionally, four infrared-reflecting markers are mounted on the anterior surface of the phantom. The locations of these markers are known precisely, making it possible to calibrate and quality-control optical tracking equipment such as is conventionally used with IGRT apparatus.